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Collimation Valery Kapin Workshop on Booster Performance and - - PowerPoint PPT Presentation
Collimation Valery Kapin Workshop on Booster Performance and - - PowerPoint PPT Presentation
Collimation Valery Kapin Workshop on Booster Performance and Enhancements 23-24 November 2015 Activities & acknowlegments to people involved 1) Booster Collimator Hardware & Control (motion tests): Charles Briegel, Salah Chaurize, Mike
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2-stage collimation system of FNAL booster
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2005 Pellico & Sullivan Booster Collimation DOE-Review Two-stage collimation was tested but is not used in operations (variable beam size and position due to e.g. “momentum cogging”) Two stage collimation system for booster designed and installed in 2004.
Design ~2001-03 with STRUCT & MARS codes by A.Drozhdin & N.Mokhov: Optimal primary foils at 400 MeV: tungstem 0.003mm (or graphite 0.15mm) Beams-doc-3734.
Instead 0.381 mm copper foil was installed
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Principle scheme of 2-stage collimation system
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Bryant, in CERN Acc. School (1992), p.174The primary collimator is followed by two secondary collimators set at
- ptimized phases for intercepting the
scattered particles. Simulations steps (as with STRUCT): Generate part. distribution on edge of Prim-Collimator (halo-particles) Scattering in material of thin P-Coll (Non-linear) Tracking scattered parts Collect lost particles on Sec-Colls and
- ther magnet apertures
halo particles => large amplitudes => Correct treatment non-linear dynamics => ~MADX Collimation system must redistribute losses to dedicated “secondary” collimators Usual “1-stage” collimation produces uncontrolled out-scattered protons => “2-stage” scheme
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Collimator placements in booster
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Restrictions for design: Not optimal phase advances; Small magnet & RFcav apertures; Bending magnets in coll system; Variable beam parameters during accelerator cycle
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Collimation system transverse layouts by A.Drozhdin
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Task started in 2014: optimal thickness of primary coll.
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- MADX code has been modified to include proton interactions with thin
primary collimators (Prim-Colls), while out-scattering from secondary collimators is neglected
- Dependence of collimation efficiency on thickness of Cu Prim-Colls at
injection energy (400MeV) within thickness range {0; 381um} has been simulated. It is quite smooth.
- Collimation efficiency grows up with the number of turns (simulated up to
100) under simulation approach that all accelerator parameters are constant (is it a case of booster ?)
- Optimal thickness of Prim-Colls for Cu is ~50um (or thinner) to reduce
losses of scattered protons in magnet apertures and pipes between primary and secondary collimators.
- ~50 mkm is much less of existing 381 um (0.015") Cu foil for both hor.
and vert. primaries
- Original STRUCT's calculations at 400 MeV corresponds to equivalent Cu
foils of ~12um
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MADX (w/o out-scattering): horizontal collimation for 2004-design
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After 10 turns Maximum N_colls_sum at 50um (within 30-60um)
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Primary thickness for ~2004 “STRUCT” design & Equiv. materials
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RMS scattering angle
[ ] [ ]
[ ]
cm g/cm g/cm
3 2
d x ⋅ = ρ
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New aluminium Prim-Colls
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Oct.2015 New simplified primary assembly (just Al plate without any ceramic insulators): R.J. Tesarek et al, Beams-Doc-5983, November 4, 2015.
2005: Cu primary heat sink with signal cable (+ceramic ins.)
From abstract: … a candidate primary collimator design of a uniform aluminum foil with a uniform thickness of 381 um. … the steady state temperature of the collimator under nominal beam conditions to be at or below 140 C (absorb <4.6W).
Aver.deposited beam power is reduced 30 times
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- Sec. collimators motion: reliability (courtesy R.Tesarek)
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- Sec. collimators motion: Horizontal Backlash Calibration
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New simulations: upgraded model
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General idea by V.Lebedev & N.Mokhov A new simulation approach including out-scattering in Sec-Colls is under development for a correct comparison
- f two-stage and one-stage collimation in the booster.
The proton interactions with Sec-Colls are simulated by MARS (Mokhov's group) and used by MADX tracker as black-boxes. Calulations for different collimator layouts (2004-design; 2011 Drozhdin “real” configuration; and find optimal one) Plans: simulations for different beam sigma and halo sizes Optional: Optimizations for existing single-stage scheme
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New simulations: Mars model for booster secondary collimators
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The model of sec. collimator was created by I. Tropin & I.Rakhno. Interface with “STRUCT” coordinate system (x,x’,y,y’,p)
One model for 3 identical sec-colls. Model is centered on ref. orbit. Transverse shifts simulated via shift of input and output particle coordinates
Steps: a) MADX multiturn tracking; b) protons lost on collimators collected at collimator fronts; c) that protons are re-tracked throughout sec-colls with MARS; d) Out-scattered protons are collected at sec-coll ends are tracked again by MADX
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Example of 1 stage horizontal collimation on COL1
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Example of 1 stage vertical collimation on COL2
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Efficiency(%) of 1 stage collimation vs sigma & halo-width
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81.61 81.93 1000um 76.40 75.48 100um 65.13 69.86 10um 4sigma 3sigma 67.45 68.04 1000um 46.05 48.71 100um 21.18 24.14 10um 4sigma 3sigma
Horizontal collimation on COL1 (Convergent beam envelope) Vertical collimation on COL2 (Divergent beam envelope)
1-stage collimation dependence on: Twiss alpha – higher absorption for convergent beam higher beam halo width => higher impact parameter Beam sigma is not critical within 3-4 for booster
Efficiency in range 25-80%; Possible optimization by yaw & pitch angles
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Loss distributions with present 381um Cu foil (10turns)
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Loss distributions with present 381um Cu foil (100turns)
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Losses on collimators redistributed with outscattering (381um Cu foil)
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Loss distributions with new 381um Al “50um Cu” foil (10turns)
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Loss distributions with new Al “50um Cu” foil (100turns)
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Losses on collimators redistributed with outscattering (new Al 381um foil)
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Efficiency(%) of 2 stage collimation vs sigma & halo-width & turns
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4sigma 3sigma 67 / 65 66 / 65 66 / 65 % of lost 51 / 65 48 / 64 48 / 63 % of injected 60 / 58 44 / 58 1000um 59 / 58 42 / 57 100um 59 / 57 41 / 55 10um % of lost % of injected halo
Horizontal collimation with new Al “50um Cu” foil at 10/100 turns 2-stage collimation dependence on: Efficiency <coll.loss>/<total losses> ~ const vs N_turns Efficiency <coll.loss>/<injected> increases with N_turns Efficiency decreases for larger beam sigma Weak dependency of halo width (?)
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Plans for near future
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- Matt made drawings for new Al foil and its “fork ” holder:
fabricated and ready for alignment measurements and installation of both(?) primaries in vacuum (a future >8hrs shutdown)
- “Easy” replacement of prim. plate (Al: 0.015”->0.005” -> ? mm-Be)
- Beam tests could be started afterwards (~Dec. 2015)
- Simulations plans (see above) include comparison with 1-stage colls
- Due to many concerns (collimation in synchrotron, not
storage/collider ring) : review of collimation systems on similar proton synchrotrons (J-PARC, SNS, ISIS, ?) to work out possible alternative solutions, if present booster two-stage collimations is failing.
- Considering alternative collimations schemes
(e.g. a’la “septum” suggested by V.Lebedev)
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Supporting slide
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- Sec. collimators motion: 6B Horizontal motion
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